 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.ui.handlers;

 import org.eclipse.core.commands.IHandler;
 import org.eclipse.core.expressions.IEvaluationContext;
 import org.eclipse.ui.internal.services.IEvaluationResultCache;

 /**
  * <p>
  * A token representing the activation of a handler. This token can later be
  * used to cancel that activation. Without this token, then handler will only
  * become inactive if the component in which the handler was activated is
  * destroyed.
  * </p>
  * <p>
  * This interface is not intended to be implemented or extended by clients.
  * </p>
  *
  * @since 3.1
  * @see org.eclipse.ui.ISources
  * @see org.eclipse.ui.ISourceProvider
  */
 public interface IHandlerActivation extends IEvaluationResultCache, Comparable {

     /**
      * The depth at which the root exists.
      *
      * @since 3.2
      */
     public static final int ROOT_DEPTH = 1;

     /**
      * Clears the cached computation of the <code>isActive</code> method, if
      * any. This method is only intended for internal use. It provides a
      * mechanism by which <code>ISourceProvider</code> events can invalidate
      * state on a <code>IHandlerActivation</code> instance.
      *
      * @deprecated Use {@link IEvaluationResultCache#clearResult()} instead.
      */
     public void clearActive();

     /**
      * Returns the identifier of the command whose handler is being activated.
      *
      * @return The command identifier; never <code>null</code>.
      */
     public String getCommandId();

     /**
      * Returns the depth at which this activation was created within the
      * services hierarchy. The root of the hierarchy is at a depth of
      * <code>1</code>. This is used as the final tie-breaker in the event
      * that no other method can be used to determine a winner.
      *
      * @return The depth at which the handler was inserted into the services
      * hierarchy; should be a positive integer.
      * @since 3.2
      */
     public int getDepth();

     /**
      * Returns the handler that should be activated.
      *
      * @return The handler; may be <code>null</code>.
      */
     public IHandler getHandler();

     /**
      * Returns the handler service from which this activation was requested.
      * This is used to ensure that an activation can only be retracted from the
      * same service which issued it.
      *
      * @return The handler service; never <code>null</code>.
      */
     public IHandlerService getHandlerService();

     /**
      * Returns whether this handler activation is currently active -- given the
      * current state of the workbench. This method should cache its computation.
      * The cache will be cleared by a call to <code>clearActive</code>.
      *
      * @param context
      * The context in which this state should be evaluated; must not
      * be <code>null</code>.
      * @return <code>true</code> if the activation is currently active;
      * <code>false</code> otherwise.
      * @deprecated Use
      * {@link IEvaluationResultCache#evaluate(IEvaluationContext)}
      * instead.
      */
     public boolean isActive(IEvaluationContext context);
 }

